Automatic switch



Nov. 22, 1938.

R. TAYLOR ET AL AUTOMATIC SWITCH Filed oct. 12, 1935 2 Sheets-Sheet l I "INVENTO/FS- Ream a0 727w? @m/PQ? 77/0/1015 BAKER Nov. 22, 1938. R. TAYLOR ET AL 2,137,422

AUTOMATIC SWITCH Filed odt. 12, 1935 2 Sheets-Sheet 2 i IIIIIIIIF M mmnF T mmuw Jmmvroes:

' Ream/Aw 7km 0/? 6,; E 7i/04Ms BAKER Patented Nov. 1938 UNITED STATES PATENT OFFlCE a '2,1a'z,4z2.' "l

. AUTOMATIC swrron Reginald Taylor, Liverpool, languid, and George Thomas Baker, Caerphilly, Wales, assignors to Associated Telephone and Telegraph Company, Chicago, 111., a corporation of Delaware Application October 12, 1935, Serial No. 44,768

' In Great Britain November 3, 1934 :16 Claims (01. 179 -18) H The present invention relates to telephone sys-. tems and automatic switches for use therein and is more particularly concerned with. improved testing arrangements for. hunting switches of the type which hunt for battery potential characterizing idle switches or other pieces of apparatus. The chief object of the invention is to provide simplified circuits giving better facilities for the transmission of booster battery metering pulses over the test conductor and ensuring that'a contact to which booster battery is connected shallnot test idle to aswitch hunting thereover.

According to one. feature of the invention in an automatic hunting switch having a free line indicatedby the presence of battery potential of one polarity on the test contacts to which contacts booster battery potential of the opposite polarity is also adapted to be applied while the associated line is in, use, a rectifier is provided in circuit with the testing means so as to distinguish between the various potentials on the test contacts and only in the event of a free line being. encountered to'arrest the switch and bring about the establishment of a through connection which connectionis adapted to be maintained as'long as either booster battery or earth potential is applied to the test lead.

Other features relate to improved arrangements for giving preference to one particular set of wipers of a large capacity switch if both encounter idle lines simultaneously and to arrangements for reducing the number of relays required by the use of a combined test and changeover relay. l

The invention will be better understood from the following description of one method of carrying it into effect, reference being had tothe accompanying drawings comprising Figs. 1 and 2 which show a group selector provided with two sets of wipers and adapted to test two groups of outlets simultaneously. l l l The switch is of the two-directional type having socalled rectangular movement in which no release magnet is provided but the restoration of theswitch to normal is effected by stepping the switch wipers forward to the end of the level and then allowing them to complete their restoration by avertical and rotary movement. A switch of this type is described in the patent of Robert N.

Saxby, No. 2,028,689, filed September 22nd, 1932.

An increase in the hunting speed is achieved byallowing the magnet to operate in a self-interrupted circuit.

When the switch is taken into use a circuit is completed between the negative and positive conductors over which relay A operates and completes a circuit for relay B. If the switch is functioning as a first selector, earth to the lower winding of relay A may be supplied by way of a dial tone transformer, as indicated by the dotted earth connection, to inform the calling subscriber that the circuit is ready to respond to the dialled impulses. 'Relay B operatesand at armature bl replaces battery fed viaresistance YA to the P wire with earth to guard the circuit, and at armature b3 lights. the individual supervisory lamp LP in circuit with the common conductor H) extending to exchange alarm equipment which provides a signal in case'the switch isseized and not operated within a predetermined time.

Upon the reception of the setting impulses, re-

lay A responds and repeats them by way of armature al to the vertical magnet VM in series with the .low resistance left-hand winding ofrelay I-IX and accordingly the wipers are raised to the desired level. Relay I-IX operates in. this circuit and at armature hxl short-circuits its right-hand winding thereby producing a slugging effect which is sufficient to hold the relay operated continuously during the impulsing period. Relay B is similarly held by reason of the copper slug on its core. As soon as thewipers leave the normal position, off-normal springs Ni and N2 are oper ated mechanically but perform no immediate function.

At the end of the vertical impulsing, relay A holds and after a short interval relay HX releases, and at armature M22 completes a selfinterrupted driving circuit to the rotary magnet RM to earth supplied over the common conductor H extending to release alarm equipment and accordingly the. wipers. are rotated in search of a free outlet in the level selected. Normal. rotarysprings NRI and NR2 are operated mechanically as soon. as the wipers commenceto rotate and completea testing circuit for relay HX to the test wiper Pl. The. testing circuit for relay HY to the test wiper P2 .isalready completed .by armature b4. 7

Idle outlets are marked in the banks PI and P2 by the presence of resistance battery on the test contacts andif it is assumed that the wiper PI is the. first to encounter a free outlet the fast opcrating test relay I-IX immediately operates over the following circuit, earth at armature bl, metal rectifier MRA, right-hand windingof relay HX,

' cause the switch to extend the call to an existing connection. At its armature 12x2 relay I-IX opens the drive circuit for the rotary magnet and at armature hat-l completes a temporary holding circuit over its lefthand winding which is sufliciently low in resistance to guard the outlet selected. Relay HX also at armature hmZ extends battery from the rotary magnet to the switching relay HA which operates and looks over its armature hill, at armature ha2 opens the test circuit to relay HY and at armatures ha, M and has extends the test lead and the negative and positive speaking leads over the upper set of wipers to the succeeding switch. Relays A, B and HX thereupon release, while the switching relay HA remains held to earth which is now fed back over the test lead from the succeeding switch.

If wiper P2 is the first to encounter a free outlet relays HY and HB operate-with similar results to those already described except that the connection is extended to the succeeding switch over the lower set of wipers. The. metal rectifier MRB has the same function in relation to relay HY that the metal rectifierMRA has in relation to relay HX.. Further, at armature hb'l a circuit is prepared to the common conductor l2 extending to a test buzzer which may be operated by short-circuiting the test jack springs T2 to indicate which set of wipers is connected up without having to remove the dust cover and examine the actual relays.

.If both test wipers PI and P2 encounter idle outlets simultaneously both test relays HX and HY operate together, but it will be noticed that relay HX at armature hxZ immediately disconnects the operating battery from relay HB thus preventing this relay from operating. RelayHA therefore operates and the upper set of wipers always receives priority under these conditions.

It will be appreciated that as relays HX and HY are employed only as test relays and that separate switching relays HA and HB- are provided, the former relays need only carry a few springs and may be designed to operate very quickly when an idle line is found. On the other hand, the switching relays HA and HB need not be quick to operate and may therefore be designed to have a greater margin in other directions, thus they may be adjusted with a heavy spring tension which causes them, to release quickly.

It will also be noted that after the metal rectifiers have fulfilled their function of guarding against seizing a line on which booster battery is present they are disconnected and a straightthrough connection is provided from the test wiper to the incoming test lead to permit the passage of booster battery metering impulses over the test lead.

Ifall outlets infthe level selected rove bus the wipers rotate to the 11th position where test relay HY operates in series with battery. fed

through resistance YA to open the driving .cir-

cult to the rotary magnet. Owing to the mechan-' ical operation of cam springs in the l1th'posi-. tion, relay HE is prevented from switching since its circuit is opened at springs S3, while at springs $2 the low resistance holding circuit to relay HY is disconnected since this would otherwisetend to shunt the common resistance marking battery YA to such an extent as to" prevent other selectors from switching through in the 11th position. Furthermore, at the make contacts of cam springs SI busy flash and tone from the cam assembly BF is extended through the lower winding of relay A to the positive line to inform the calling subscriber that the connection is unavailable. During the flash period, relay A is released Earth is also connected to wiper Pl by cam springs S3 to operate an overflow meter (not shown) connected to the 11th bank contact.

Upon the release of the connection at the end of the conversation relay HA or HB, as the case may be, releases whereupon the self-interrupted driving circuit is again completed to the rotary magnet RM from earth on the common conductor l I extending tothe alarm equipment, and accordingly the wipers are rotated clear of the banks after which they fall and restore backwards below the banks to their normal position. The off-normal springs N2 now release and open the homing circuit while battery is again connected to the test conductor via resistance YA to mark the switch as idle. Preferably during the vertical release movement of the wipers the rotary magnet is mechanically prevented from opening its interrupter contacts so that there is no tendency for it to chatter.

In case for any reason the switch fails to restore, the off-normal springs N2 remain closed and as the result of the continued connection of battery to conductor H the alarm equipment functions after a delay period and provides an indication of the faulty condition.

Terminals marked TI to T8 in the drawings. are assembled in the form of a test jack located at the front of the switch to facilitate testing.

. The condenser QA and associated resistance is for the purpose of preventing arcing taking place at the interrupter contacts associated with the driving magnets.

We claim:

1. In an automatic switch arranged to be driven over outlets responsive to the closure of a driving circuit, a combined test and guard relayeffective to test for idle-indicating potential on the test conductor of an idle outlet, contacts'on said relay closed when the relay energizes over the test conductor-of an idle outlet for closing a low-resistance guarding circuit through a winding of the relay to apply guarding potential to the test conductor of the outlet, a switching-through relay, and additional contacts on the combined test and guard relay for opening the driving circuit and for energizing the switching-through relay.

2. In a free-hunting automatic switch having a driving circuit, means for closing the driving circuit to cause the switch tohunt over a group of outlets, afirst relay in the switch and means for energizing it over the test conductor of an idle outlet,-a switching-through relay for switching through to the idle outlet, contacts operable by the first relay upon energization for applying a guarding potential to the test conductor of the outlet found to be idle, and other contacts operable by the said first relay upon the energization thereof to open the driving circuit and to operate the said switching-through relay. 7

3. In a free-hunting automatic switch wherein, test conductors of outlets are tested successively during the hunting movement of the switch and wherein the hunting movement of the switch is terminated and a switching-through operation is performed when an idle outlet is found, a quick-acting test and guard relay and a switching relay, means for operating the quick-acting test and guard relay immediately over the test conductor of an idle outlet to place a guarding potential on the outlet and to terminate the driving movement, and means for subsequently operating the switchingthrough relay to extend connection tothe outlet found to be idle.

4. In a two-motion automatic switch having a control relay, means in the switch for maintaining said control relay operated during the primary movement and for restoring it to start the secondary movement, outlets successively engaged during the secondary movement, and means for re-operating said control relay over the test conductor of an idle outlet to terminate the secondary movement. i

5. In a two-motion automatic switch having a control relay and having groups of outlets,

each outlet having a test conductor adapted to be engaged by a test wiper of the switch during the secondary movement, means in the switch for maintaining the control relay operated during the' primary movement and for restoring it at the end of the primary movement to start the secondary movement, and means for re-energizing said relay over the test wiper of the switch and the test conductor of an idle outlet to terminate the secondary movement when an idle outlet is found.

6. In an automatic switch having alternative sets of wipers, each set of wipers having access to a. different set of outlets, means for driving the wiper sets over their associated outlets, each wiper set including a test wiper adapted to cooperate with test contacts of the associated outlets, there being also a separate test relay for each wiper set and a separate switching-through relay, means effective when either wiper set engages an idle outlet for energizing the test relay of such wiper set over the associated test wiper and the test contact of the idle outlet, contacts on the test relay for operating the associated switching relay, and contacts on one test relay for opening the circuit of the switching relay associated with the other test wiper, whereby one set of wipers is given preference over the other in the event that both wiper sets encounter idle outlets at the same'time.

'7. In combination, an automatic hunting switch having access to a group of outlets and to an additional outlet used as an overflow outlet in case the otheroutlets are all engaged, each of the outlets having a test contact on which an idle-indicating potential is maintained while the outlet is idle, said switch having a test wiper and a combined test and guard relay, means for operating said relay over the test wiper and the test contact of an idle outlet to terminate the driving movement of the switch and to apply a guarding potential to the test contact, and additional means effective with the arrival of the selector on the said overflow outlet for preventing the application of guarding potential to the overflow outlet, whereby the overflow outlet is not marked engaged to the other switches having access to it.

8. An automatic hunting switch having a free line indicated by the presence of battery potential of one polarity on the test contacts to which contacts booster battery potential of the opposite polarity is also adapted to be applied while the associated line is in use in which a rectifier is provided in circuit with the testing means so as to distinguish between the various potentials on the test contacts and only in the event of a free line being encountered to arrest the switch and bring about the establishment of a through connection which connection is adapted to be maintained as long as either booster battery or earth potential is applied to the test lead.

9. An automatic hunting switch including a test relay adapted to distinguish between normal battery potential and booster battery potential and a switching relay arranged to be operated responsive to the operation of said test relay and to remain operated independently thereof.

10. An automatic hunting switch including a test relay arranged to operate over a high resistance winding and a low resistance winding in series when an idle line is encountered and thereupon to shunt its high resistance winding to guard said line in which the switch includes also a switching relay for maintaining a straightthrough connection from the incoming test lead to the test wiper throughout the connection.

11. An automatic hunting switch including a test relay arranged to operate over a high resistance winding and a low resistance winding in series when an idle line is encountered and thereupon to shunt its high resistance winding to guard said line in which said relay is also arranged to initiate the automatic hunting movement after the switch has responded to a series of impulses.

12. An automatic switch as claimed in claim 10 in which the test relay is provided with one armature for shunting its high-resistance winding and with a second armature arranged to open the driving circuit and complete a circuit for the switching relay.

13. An automatic switch as claimed in claim 9 provided with two sets of wipers in which a separate test relay is associated with each set of wipers and is arranged to control a corresponding switching relay.

14. An automatic switch as claimed in claim 9' in which an overflow contact is provided at the end of a group of contacts and is marked with idle-indicating potential to cause the switch to select said contact when all the preceding contacts in the group are busy.

15. In an automatic switch, a test relay operated when the test wiper of said switch encounters a contact connected to one pole of battery, a switching relay, means controlled responsive to the operation of said test relay for operating said switching relay, and means controlled by said switching relay for providing a holding circuit therefor when the opposite pole of battery is connected to said contact.

16. In an automatic switch in which the wipers are directively controlled in a vertical direction to select a particular level of bank contacts and automatically rotated thereover to search for an idle trunk line, a test relay adapted to distinguish between exchange battery, ground, or booster battery potentials; a switching relay and an operating circuit therefor, said test relay operated only when the test wiper of said switch encounters exchange battery potential on an associated bank contact in a selected level to terminate the automatic rotation of the wipers and to complete the operating circuit for said switching re- 

